Process for improving phosphorous removal in waste water treatment without chemical addition

ABSTRACT

A wastewater treatment process wherein a portion of a mixture of influent waste water and biomass are transferred from a first anaerobic region to a second anaerobic region having a relatively long retention time in order to produce additional very short chain fatty acids therein which are thereafter returned to the first anaerobic region so that biomass therein takes up the very short chain fatty acids. The contents of the first anaerobic region thereafter flow downstream into an aerobic region wherein the biomass takes up phosphorus. A portion of the biomass is returned to the first anaerobic region and a second portion of the biomass is wasted with phosphorus therein, thereby removing phosphorus from the wastewater being treated.

BACKGROUND OF THE INVENTION

The present application is directed to a process for the biologicaltreatment of wastewater to remove organic matter, especially whilereducing the phosphorus content of the effluent water without addingadditional chemicals for the phosphorus removal.

Wastewater treatment has progressed substantially in the last fiftyyears. Early treatments utilized various chemicals to rid the wastewaterof organic material. Subsequently, most chemical treatments have beensurpassed by use of microorganisms which through various processesconvert organic impurities in the water to various combinations ofcarbon dioxide, methane, water and inorganic nitrogen and phosphoruscompounds.

While microorganisms are effective in reducing organic content,phosphorus and nitrogen often present problems in effluent water frombiological processes. The present application is especially directed toan improved process for the removal of phosphorus from the water.

Phosphorus presents an eutrophic problem in that it substantiallyenhances the growth of aquatic plant life such that an influx ofphosphorus may cause sufficient plant growth in streams or lakes to killfish or produce other problems. Phosphorus is also a common component ofhuman or animal waste and of many household or industrial products ofthe type that are likely to become a component of waste water collectedin a city's sewer system, such as soap for washing clothes whereinphosphorus is used as whitener.

Previous processes have been developed to try to rid effluent fromwastewater treatment plants of phosphorus. For example, one processwherein biomass and wastewater are mixed in an aerated tank is generallyknown as the Phostrip process. In the Phostrip process the biomass withsome uptake of phosphorus in the bacteria is separated from theclarified water. The separated biomass is then subjected to an anaerobiccondition in a thickener or stripper. In the stripper phosphorus isreleased by the bacteria and a phosphorus rich decant is removed fromthe stripper and treated with lime to remove the phosphorus. The biomassis then returned to the aerated tank to mix with incoming wastewater.This process has varying degrees of success, but requires the chemicaladdition of lime in order to work.

In 1974 the inventor of the present application discovered thatplacement of an unaerated zone or region upstream of an aerobic regionin an activated sludge process would result in phosphorus uptake by thebacteria when in the aerobic region. This process is generally referredto as the Phoredox process. However, high phosphorus removal with thisprocess was not successful with all influent waste water streams.

Subsequently, Fuhs and Chen in trying to understand the mechanism ofphosphorus uptake by bacteria suggested that certain microorganisms(phosphate accumulating organisms), while obligate aerobic organisms,could take up and store certain short chain volatile fatty acids,especially acetic acid and propionic acid in an anaerobic treatmentregion and later use the fatty acids to take up phosphorus that isstored in the bacteria as polyphosphate in an aerobic treatment region.In theory the microorganisms store polyphosphate as an energy source inthe aerobic region and release the energy stored in the polyphosphatelater by breaking high energy phosphate bonds creating surplusphosphates which are released in a preceding non aerated region.Thereafter, if short chain fatty acids are available in an anaerobicregion, the acids are stored in certain bacteria as an intermediateproduct, such as poly-β-hydroxybuterate (PHB). As the biomass passes tothe aerated region, the microorganisms that have stored the organicacids metabolize the PHB and use the energy gained to again take upphosphorus from the surrounding liquid. Within the theory of thisprocess the microorganisms will take up more phosphorus in the aerobicregion than is released in the anaerobic region, if sufficient amountsof the short chain fatty acids are available. Thus, in theory, if excessbiomass is wasted, then the phosphorus in the influent wastewater shouldbe wasted with the wasted biomass. If insufficient fatty acids arepresent, then the phosphorus will remain outside the biomass and will bedischarged with the effluent water.

While certain actual treatment facilities do receive wastewater withsuch short chain fatty acids in sufficient quantity to produce at leastsome phosphorus reduction, many have little or do not have enough toremove most or at least a substantial amount of the phosphorus. Theshortage of short chain fatty acids can be made up by addition of thefatty acids from an external source, but this is a comparativelyexpensive and undesirable chemical addition.

Consequently, applicant has found a need for a method of biologicallyproducing such short chain fatty acids within the biological process andhas found a simple and surprisingly effective method and apparatus fordoing so.

SUMMARY OF THE INVENTION

A process and apparatus are provided to improve the removal ofphosphorus from a waste water stream without requiring the addition ofchemicals to achieve improved phosphorus removal. In particular, in thetreatment of the wastewater, the water is first directed to a firstanaerobic region, zone or basin wherein the influent wastewater is mixedwith biomass containing microorganisms that has been removed frompreviously treated wastewater and partially recycled to the firstanaerobic region. The biomass prior to being recycled to the firstanaerobic region is comparatively starved for organic food in that ithas not been exposed to an organic food source since entering thebiomass recycling system. Also, the biomass prior to being recycled tothe first anaerobic region contains a comparatively high amount ofphosphorus that is available to provide energy to the bacteria in thebiomass. In the first anaerobic region, the biomass mixes with andabsorbs organic food material contained in the influent wastewater. Aportion of the organic food material in the wastewater is normally shortchain volatile fatty acids, especially acetic acid and propionic acidand this term is intended to include intermediaries of such acids. Theseshort chain fatty acids are especially important in the process of thepresent invention, because when these acids are metabolized in asubsequent aerobic region, the fatty acids provide energy needed for thebiomass to uptake and store phosphorus. If the fatty acids are notpresent in sufficient quantity then the phosphorus that is contained inthe incoming biomass may not be taken up later by the biomass nor willthe phosphorus in the influent wastewater be taken up, so that thephosphorus that is not later taken up will pass through with the waterand will be discharged with the effluent water stream. Some influentwastewater streams have insufficient short chain fatty acids to allowthe biomass to later take up the phosphorus or only enough to take upsome of the phosphorus. The process of the present invention allowsfacilities treating wastewater that are deficient in short chain fattyacids to achieve very good biological phosphorus removal withoutrequiring chemical addition to chemically remove the phosphorus or torequire the addition of fatty acids from an outside source.

In the first anaerobic region, solids retention time is such thatcertain microorganisms in the biomass that contain phosphorus utilizethe phosphorus to produce energy and in so doing release at least someof the stored phosphorus into the fluid within the first anaerobicregion.

While the phosphorus is being released, a side stream of thebiomass-wastewater mixture (mixed liquor) is removed from the firstanaerobic region, preferably on a continuous basis and directed to asecond anaerobic region, zone or basin wherein the flow rate and solidsretention is slowed compared to the first anaerobic region. For example,the first anaerobic region may have a flow rate calculated to provide asolids retention time that will in turn produce a biomass concentrationof 2000 to 4000 milligrams per liter, whereas the biomass concentrationin the second anaerobic region is preferably in the range from 7000 to25,000 milligrams per liter. Preferably, the side stream enters near thebottom of the second anaerobic region and flows upwardly therethrough.

In the second anaerobic region, it is preferably desirable to have theflow rate sufficiently slow to allow a biomass blanket to form on thebottom of the region and to fill the second anaerobic region to thelevel where the fluid therefrom flows out of the second anaerobicregion. The flow from the second anaerobic region is returned to thefirst anaerobic region, although the flow from the second anaerobicregion is returnable to near the same locations from which is waswithdrawn from the first anaerobic region or, for example, the returnflow can be returned to a downstream location in the first anaerobicregion so that the short chain fatty acids produced in the secondanaerobic region is mixed with the biomass before entering an aerobicregion.

In the second anaerobic region, certain microorganisms in the biomass inan anaerobic process convert or ferment longer chained organic compoundsin the wastewater to the desired very short chain volatile fatty acidsincluding, especially acetic acid and propionic acid and relatedcompounds. While it is desirable for the biomass to build up in thesecond anaerobic region, it is also desirable for the short chain fattyacids to flow through and be washed or carried by the outflow from thesecond anaerobic region to the first anaerobic region.

When the short chain fatty acids are received in the first anaerobicregion, the microorganisms in the first anaerobic region that have usedthe phosphorus therein to produce energy and that have expelled at leasta portion of the phosphorus, take up, acquire or absorb the short chainfatty acids that were produced in the second anaerobic region withoutmetabolizing the fatty acids in an oxygenated process.

Subsequently, the mixed liquor from the first anaerobic region is flowtransferred downstream to an anoxic region and, thereafter, to an oxicor aerobic region. In the oxic region, the short chain fatty acids thatwere acquired by the microorganism or stored therein or therewith, aremetabolized utilizing oxygen to produce energy. After the metabolizationof the short chain fatty acids, it is theorized that the associatedmicroorganisms then have sufficient energy to again take up phosphorusfrom the mixed liquor and store this phosphorus in a form having highenergy phosphate bonds. The amount of phosphorus taken up by the biomassin the oxic region, provided that there is sufficient short chain fattyacids present in the first anaerobic region, is greater than wasreleased in the first and second anaerobic regions, so not only is thephosphorus that was released in the anaerobic regions reacquired, butalso a major portion or all of the phosphorus that was contained in theincoming wastewater is taken up by the biomass. This is possible partlybecause the quantity of the biomass has grown and is greater by the timethe biomass flows downstream from the anaerobic regions to the oxicregion as compared to the biomass that was recycled to the firstanaerobic region, but more so because of the energy gain in the biomassthat subsequently results from sufficient short chain fatty acids beingpresent in the anaerobic region in accordance with the presentinvention.

Some of the effluent from the oxic region may be recycled to the anoxicregion. The remainder of the effluent of the oxic region flowsdownstream to a clarifier wherein flow rates are slowed and the biomassis allowed to settle due to gravity in a quiescent region and becomeseparated from clarified water. A portion of the biomass from theclarifier is wasted to storage or transferred to another process forfurther processing and the remainder is preferably recycled to the firstanaerobic region. Preferably, the recycled biomass flows first through apreanoxic region and thereafter to the first anaerobic region to removenitrates in the biomass. The clarified water with a consequentcomparatively low or no phosphorus content is discharged from theprocess.

It is also noted that certain wastewater includes nitrogen compoundsthat are present in the influent or that are formed by operation of themicroorganisms on organic material containing nitrogen. The presentprocess is cooperatively usable with conventional nitrogen removalstages or processes.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, the objects of the present invention are to provide anapparatus for use in waste water treatment for operably removingphosphorus from influent waste water being treated and that hasinsufficient short chain fatty acids to support substantial phosphorusremoval utilizing microorganisms and without requiring chemical additionfor the phosphorus removal; to provide such an apparatus having a firstanaerobic region for mixing influent waste water and recycled biomass toform a mixed liquor and a second anaerobic region with associated flowconduits and pumps or the like to allow a portion of the mixed liquor tobe transferred from the first to the second anaerobic region wherein thesolids retention rate is increased in comparison to the first anaerobicregion and wherein fermentation processes produce short chain volatileorganic acids which are thereafter returned to the first anaerobicregion for uptake by microorganisms therein; to provide such anapparatus having an oxic region flow located downstream from the firstanaerobic region for aerobically treating the mixed liquor so thatcertain microorganisms that have stored short chain fatty acids as PHB,metabolize the PHB and, thereafter, uptake phosphorus; to provide suchan apparatus having a settling region for separating biomass fromclarified water downstream of the oxic region and from which a portionof the separated biomass is wasted and the remainder is returned to thefirst anaerobic region; to provide such an apparatus including structurefor operably reducing nitrogen containing compounds in the waste waterthat acts cooperatively with the remainder of the apparatus; to providea method to be used in conjunction with the above noted apparatus thatallows removal of all or a large portion of phosphorus from a wastewater stream that has insufficient short chain fatty acids to providefor such removal and wherein the process does not require addition ofchemicals such as lime, metal salts or short chain fatty acids from anexternal source in order to achieve relatively high phosphorus removalso that effluent water is relatively low in phosphorus content; and toprovide such an apparatus and method which are environmentallybeneficial, are easy to use for their intended purpose, arecomparatively inexpensive relative to other processes that removephosphorus and are especially well adapted for the intended use thereof.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a waste water treatment apparatus,especially adapted for the removal of phosphorus from the waste water inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

The reference numeral 1 generally designates a waste water treatmentfacility. Waste water from city collection sewers, industrial sewers orother sources of wastewater including organic material and phosphoruscontaining compounds, is collected or fed directly into the facility 1from a waste water influent region generally identified by the referencenumeral 4. Effluent clarified water is discharged from the facility 1 toa discharge region generally identified by the reference numeral 5. Thedischarge region 5 may be a holding tank or the clarified water ispreferably discharged to a stream, lake or the like.

A first anaerobic basin, tank, zone or region 10 is provided topreferably receive all of the influent wastewater from the region 4through flow conduit 6. However, in certain wastewater treatmentprocesses a portion of the influent wastewater may be directed to otherregions for cooperate treatments or for alternative reasons. Alsopreferably, the flow of wastewater into the region 10 is continuous andthe first anaerobic region 10 is constructed such that the influentwastewater generally enters the first anaerobic region 10 on one sideand flows to the other side. Alternatively, or in addition, it isforeseen that the influent wastewater may enter from the top or bottomand exit the opposite or any alternative flow configuration to provide apass through flow pattern. The anaerobic region 10 is sized to handle anexpected average volume of influent wastewater and this in combinationwith the flow path allows design of the first anaerobic region 10 suchthat the influent wastewater flows through the first anaerobic regionwith a preselected calculated and preferred solids residence timetherein. For example, a preferred solids retention for the firstanaerobic region 10 is between 2000 and 4000 milligrams per liter ofbiomass solids, although it is foreseen that this may be variedaccording to site and operational circumstances. A hydraulic retentiontime within the first anaerobic region 10 is preferably between about0.5 and 2.0 hours. The anaerobic region 10 (as with the other regionsdiscussed herein) may be clearly defined by the structure such as a tankor basin or may be simply a part of a flow channel through which thewater flows and wherein different regions are defined by the processthat occurs in the regions. Likewise, conduits may be specific pipes orother flow directing structure such as overflow weirs and the like.

In the anaerobic region 10, the waste water is mixed with recycledbiomass which results from processing which will be discussed furtherbelow, so as to form a mixed liquor of living biomass and waste water tobe treated. The anaerobic region 10 does not have added oxygen and ispreferably entirely free of nitrates or is sufficiently lacking inoxygen that bacteria in the biomass can not take in sufficient oxygen tosignificantly perform oxygenated metabolic processes.

The biomass that is recycled to the first anaerobic region 10 iscomparatively starved for organic food, such as is found in thewastewater. This biomass also includes a wide variety of microorganismsat least some of which are capable of fermenting organic material in theabsence of oxygen and some of which are capable of metabolizing organicmaterials to carbon dioxide and water in the presence of oxygen. Thebiomass specifically includes microorganisms, such as Acinetobacter sppthat are phosphate accumulating organisms. The phosphate accumulatingorganisms while in the first anaerobic region 10 utilize energy storedin phosphorus bonds within the organism phosphorus compounds therein toproduce energy in the absence of oxygen and subsequently both releaseexcess resulting phosphates into the waste water and absorb volatileshort chain fatty or organic acids (including acetic and propionicacid), if such acids and related compounds are present in the water. Theorganic acids are believed in theory to be temporarily taken up withinthe microorganisms while in the first anaerobic region 10.

A portion of the mixed liquor is removed from the anaerobic region 10and transferred to a second anaerobic region 12 that is also referred toby the term “anpref” region, because the second anaerobic region 12 ismaintained under anaerobic conditions and functions as a prefermenter.

Flow passes from the first anaerobic region 10 to the second anaerobicregion 12 through a conduit 14 and is driven and controlled by a pump15. Flow returns from the second anaerobic region 12 to the firstanaerobic region 10 through a conduit 16. Preferably, the flow in thesecond anaerobic region 12 enters near the bottom and exits near the topthereof. Furthermore, the second anaerobic region 12 is sized and theflow rate thereinto is selected so that flow through the secondanaerobic region 12 is comparatively slow and solids retention time(SRT) is comparatively high compared to the first anaerobic region 10,such that biomass collects therein and forms a blanket that rest on thebottom of the second anaerobic region that preferably fills the secondanaerobic region 12. Normally the blanket will fill the second anaerobicregion 12 to overflowing.

Preferably, the flow rate through the second anaerobic region 12 isselected and the second anaerobic region 12 is sized so that theconcentration of the biomass is between 7,000 and 25,000 milligrams perliter therein. Because of the substantially oxygen free and fermentingconditions in the second anaerobic region 12, certain and variousorganic compounds found in the wastewater are reduced to simple andrelatively short chain fatty acids (especially acetic acid and propionicacid and intermediaries thereof). The short chain fatty acids aregenerally volatile and are more easily “washed” or urged through theanaerobic region 12 in comparison to the larger and entangledmicroorganisms in the biomass therein by the comparatively slow flowrate through the second anaerobic region 12, so as to wash the shortchain fatty acids over into the first anaerobic region 10 through theconduit 16. The conduit 16 can be provided with multiple outlets orother mixing devices to improve disbursement of the fatty acids withinthe wastewater in the first anaerobic region 10.

It is theorized in accordance with the invention that the microorganismsthat have utilized the energy from phosphorus bonds and discharged thephosphorus in the anaerobic regions, then take up the short chain fattyacids in the anaerobic regions and may store such for later use,sometimes as intermediate products especially poly-β-hydroxy buterate(PHB).

While the second anaerobic region 12 is depicted and described asreceiving and discharging through conduits, it is foreseen that the flowcould be directed by or through various types of structures oroverflows. Furthermore, while a pump is shown in the illustratedembodiment to urge flow through the second anaerobic region 12, thesecond anaerobic region 12 could be below, level with or above the firstanaerobic region 10 so that gravity can be used in certain instances todirect flow. Still furthermore, flow can be urged by other types of wellknown devices that perform the equivalent function.

In many waste water treatment facilities of the type described hereinflow rates are such that the concentration of biomass in the firstanaerobic region 10 is on the order of from 2000 to 4000 milligrams perliter, although as noted above variation outside this range occurs atcertain locations. Preferably, also as noted before the biomassconcentration in the second anaerobic region 12 is within a range from7000 to 25,000 milligrams per liter. This increased concentrationindicates that the solids retention time of the second anaerobic region12 is greater in comparison to the first anaerobic region 10.

It is foreseen under the invention that alternative systems may beemployed to create an anaerobic region wherein biomass is located insuch a manner that increased fermentation will occur due to biologicalactivity and that very short chain fatty acids will be produced prior topassage of mixed liquor into an anoxic or aerobic region. In thismanner, the fatty acids cooperate with certain microorganisms to releasephosphorus and take up the fatty acids in the anaerobic region, suchthat a rebound effect will occur at a downstream location in thepresence of oxygen where the microorganisms will respire and metabolizeorganic material using oxygen therein and thereafter take up phosphorusfrom the surrounding mixed liquor and store the phosphorus with highenergy within the cells of certain microorganisms in the biomass. It isforeseen that in some instances, the second anaerobic region could havea low level of organic food and given sufficient time that the biomassitself provides the food source.

It is also foreseen that the second anaerobic region 12 may be fittedwith a mixer that would not be utilized during normal operation butwhich may be operated from time to time to reposition biomass therein. Apump could also be used for this purpose by directing circulating flowinto multiple locations near the bottom of the second anaerobic region12.

It is further foreseen that first anaerobic region 10 may also bedivided into subregions with the flow to the second anaerobic region 12coming from a different subregion than the subregion receiving returnflow.

Downstream of the second anaerobic region 12 is an anoxic region 18joined to the first anaerobic region 10 by a conduit or flow channel 20.Operably, the anoxic region 18 is utilized in a well known andconventional manner to remove nitrates from the mixed liquor therein.

The mixed liquor is subsequently directed from the anoxic region 18 toan aerobic region 22 through a conduit or flow channel 23. In theillustrated embodiment, the aerobic region includes five oxic or aerobicsubregions 25 to 29. It is foreseen that the number of oxic regions mayvary greatly in accordance with the needs of the particular site. Theaerobic region 22 includes mixers and is operated in a well known mannerso as to inject oxygen by sparging oxygen or air into the liquor, byspraying liquor into the air, or the like, so that oxygen or airincluding oxygen enters the aerobic region 22 while mixed liquor in theaerobic region 22 is being mixed. A portion of the mixed liquor exitingthe aerobic region 22 is preferably returned to the anoxic region 18through conduit or flow path 33 under control of pump 34. For example,preferably between 50% and 60% of the outflow of the region 22 may bereturned to the region 18 so that any nitrates formed in the aerobicregion 22 may be reduced in the anoxic region 18 the anoxic region 18 ismixed but not aerated.

In the aerobic region 22, certain of the microorganisms in the biomasstherein take up oxygen through respiration and convert organic materialto carbon dioxide and water. Also, certain of the microorganisms in thebiomass take up phosphorus from the surrounding liquor. Because thebiomass grows between recycle and the return thereof to the aerobicregion 22, but much more importantly, because the organisms taking upphosphorus have sufficient stored food from the short chain fatty acidsin the form of PHB absorbed in the first anaerobic region 10, thebiomass and, in particular, the phosphorus accumulating organism in thebiomass in the aerobic region 22 takes up more phosphorus than isreleased in the anaerobic regions 10 and 12 provided that the shortchain fatty acids are available in the first anaerobic region 10. Thus,the microorganisms in aerobic region 22 preferably take up what wasreleased in all anaerobic regions plus up to 99% of all of thephosphorus coming into the facility 1 with the wastewater influent.

Discharge from the region 22 is directed through conduit or flow channel35 to a clarifier 36. The clarifier 36 is not mixed and flow rates aresufficiently slow to allow the biomass to become quiescent and settle tothe bottom of the clarifier 36 and clarified water to raise to the top.The clarified water is directed through a channel 40 to the clarifiedwater discharge region 5.

The biomass in the collected solids blanket at the bottom of theclarifier 36 is directed to a conduit or flow channel 43 whichbifurcates into a wasted or sludge stream to wasted biomass storage 45and a recycle biomass stream 46 and is urged therethough by a pump 47.The amount of biomass wasted each day is approximately equal to theadditional biomass made each day by the process, that is, the growthportion of the biomass once the facility 1 has achieved steady stateconditions, so as to continue to operate under such steady stateconditions.

The recycled biomass in the flow stream 46 is directed under flow fromthe pump 47 to a pre-anoxic region 50. The pre-anoxic region 50 has noadded oxygen and is positioned and operated in such a manner as toremove nitrates that are in the biomass by known processes. The biomassflows from the pre-anoxic region 50 through a conduit or flow channel 51to the first anaerobic region 10 to be mixed with the influent wastewater. A return line 52 flows some mixed liquor from the first anaerobicregion 10 to the pre-anoxic region 50.

It is foreseen under the scope of the invention that a fraction of theinfluent wastewater may be directed directly to the second anaerobicregion or may be mixed with the slip stream from the first anaerobicregion to the second anaerobic region. Preferably, the fraction ofwastewater directed to the second anaerobic region without passingthrough the first anaerobic region would be less than about 10 percentof the total influent wastewater flow. The mixture of flows to thesecond anaerobic region in this manner may be utilized to control thedetention time in the second anaerobic region so as to improve volatileshort chain fatty acid production. The addition of influent waste waterto the second anaerobic region without passing through the firstanaerobic region assists in elutriating the volatile short chain fattyacids from the second anaerobic region in this manner, while notdecreasing the solids retention time.

The following example is provided for the purpose of demonstrating theinvention and is not intended to limit the scope of the invention or theclaims of this application.

EXAMPLE

A pilot facility was constructed in accordance with the layout shown inFIG. 1 which was utilized to treat wastewater. The facility was operatedsequentially in a first mode and thereafter in a second mode.

In both modes of operations, the influent flow rate was 50 cubic metersof waste water per day. Further, an average the flow in channel 20 was75 cubic meters per day, the flow in channel 23 was 175 cubic meters perday, the flow in channel 35 was 75 cubic meters per day, the flow inrecycle channel 33 was 100 cubic meters per day, the flow in effluentchannel 40 was approximately 50 cubic meters per day, the flow inrecycle sludge channel 46 was 25 cubic meters per day, the flow inchannel 51 was 40 cubic meters per day and the flow in channel 52 was 15cubic meters per day.

The pilot facility was operated in mode 1 for one year. In mode 1, allflow to the second anaerobic region 12 and through channels 14 and 16was prevented by effectively removing region 12 from the facility byblocking channels 14 and 16.

The typical influent COD (amount of organic and oxygen using mattermeasured as chemical oxygen demand) was approximately 300 milligrams perliter and the influent had a particulate and colloidal fraction ofapproximately 60%. The first anaerobic region 10 had a volume of 2.07cubic meters. The mixed liquor in the first anaerobic region 10 hadmixed liquid solids averaging approximately 3000 milligrams per literand the total mass of COD entering the first anaerobic region 10 withthe influent wastewater averaged approximately 9 kilograms per day. Thephosphorus entering with the influent wastewater averaged approximately4 milligrams per liter. The average mass of solids in the firstanaerobic region 10 at any time was approximately 2.07 kilograms.

During the year of operation in the first mode, the facility experienceda non rainy season and a rainy season. During the rainy season, theconcentrations of non water components in the wastewater were highlydiluted due to large amounts of rain water. During the non rainy season,the phosphorus content in the effluent clarified water was approximately0.5 milligrams per liter following an influent phosphorus concentrationof about 4 milligrams per liter. However, acetate was required as achemical addition in the amount of between 5 and 10 milligrams per literof influent wastewater in order to obtain such reduction in phosphoruslevel.

Subsequent to operation in the first mode, the facility was operated inthe second mode. In the second mode, the second anaerobic region 12(anpref region) was flow connected to the facility and flow was allowedthrough channels 14 and 16. The second anaerobic region had a volume of3 cubic meters. Flow from the first anaerobic region 10 to the secondanaerobic region 12 (and back) was 1.5 cubic meters per day and thedaily transfer of solids from the first anaerobic region 10 to thesecond anaerobic region 12 averaged approximately 4.5 kilograms per day.Approximately 0.27 kilograms of COD was absorbed by the biomass in thesecond anaerobic region 12 each day. The mass of the solids in thesecond anaerobic region 12 averaged approximately 75 kilograms at anytime.

The ratio by weight of volatile suspended solids (VSS) to totalsuspended solids (TSS) in the mixed liquor in the first anaerobic region10 and as transferred to the region 12 averaged approximately 0.78.While in the second anaerobic region 12, approximately 25 percent of theVSS was fermented by the biomass to volatile organic acids. The ratio ofthe VSS to COD in the biomass in the second anaerobic region 12 averagedapproximately 1.42 by weight. As noted before, the flow rate through thesecond anaerobic region 12 was approximately 1.5 cubic meters per day.The average daily production of volatile organic acids produced byfermentation in the second anaerobic region 12 averaged approximately0.8775 kilograms per day and approximately 0.24 kilograms per day ofvolatile organic acids were produced in the first anaerobic region 10for a total of about 1.1475 kilograms per day of short chain fatty acidsentering the first anaerobic region 10 from all sources.

For a process of this type it is calculated that volatile organic orfatty acids in an amount approximately 4 times the mass of influentphosphorus is required in order to provide a high degree of phosphorusremoval in accordance with the present invention. Total influentphosphorus level (phosphorus in the influent wastewater) at the time ofoperation of the second mode averaged approximately 0.25 kilograms perday which in theory required approximately 1.00 kilograms per day ofvolatile organic acids in the first anaerobic region 10 to complete thebiological phosphorus process and which was calculated to be exceededduring operation. During operation under the second mode the solublephosphorus level in the effluent averaged approximately 0.03 milligramsper liter of clarified water with a total removal efficiency averagingbetween 80 and 97% during the year period of operation. During the rainyportion of operation under the second mode, it was difficult to maintainsufficient COD and phosphorus to demonstrate effectiveness and for partof the rainy period, additional amounts of each were added to allowcontinued study. During operation in the second mode, no acetate had tobe added to effect substantial phosphorus removal.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1. A process for biologically treating wastewater comprising the stepsof: a) flowing influent wastewater with organic components therein intoa first anaerobic region; b) measuring the average phosphorus content byweight of said influent wastewater; c) measuring the average short chainfatty acid content by weight of said influent wastewater; d) mixing theinfluent wastewater in said first anaerobic region with a microorganismbiomass to form a mixed liquor; e) flowing a portion of the mixed liquorinto a second anaerobic region wherein said biomass ferments portions ofsaid organic components so as to produce short chain fatty acids; f)ensuring that the flow of mixed liquor to said second anaerobic regionis sufficient to produce enough short chain fatty acids in said secondanaerobic region that when combined with the short chain fatty acids insaid influent wastewater the total is greater than four times the amountof phosphorus in said influent wastewater by weight; g) returning liquidfrom said second anaerobic region with said short chain fatty acidstherein to said first anaerobic region wherein phosphorus is releasedfrom microorganisms in said biomass in said mixed liquor and short chainfatty acids are taken up by the microorganisms in said biomass; h)thereafter flowing mixed liquor from said first anaerobic region to anaerobic region wherein said short chain fatty acids are metabolized bythe microorganisms in said biomass and phosphorus is absorbed by saidmicroorganisms; I) thereafter transferring said mixed liquor to aclarifier region wherein clarified liquid is separated from saidbiomass; and j) returning at least a portion of the separated biomasswith phosphorus therein to said first anaerobic region.
 2. In a processfor treating wastewater by mixing the wastewater with biomass to form afirst mixed liquor in a first anaerobic region and thereafter treatingthe mixed liquor in an aerobic region; the improvement comprising thestep of: a) prior to said wastewater entering said first anaerobicregion diverting a first portion of said wastewater directly to a secondanaerobic region wherein a second mixed liquor is subjected to a lowerflow rate than in said first anaerobic region and thereafter returningthe mixed liquor from said second anaerobic region to said firstanaerobic region; and b) flowing a remaining second portion of thewastewater directly to said first anaerobic region.
 3. The processaccording to claim 2 including: a) selecting said slip stream as lessthan about 10% by weight of a total wastewater flow.
 4. A process forbiologically treating wastewater comprising the steps of: a) collectingwastewater for treatment in a waste water influent region; b) flowinginfluent wastewater from said waste water influent region with organiccomponents therein directly into a first anaerobic region and mixing thewastewater therein with a microorganism biomass to form a mixed liquor;c) flowing a portion of the mixed liquor into a second anaerobic regionwherein said biomass ferments portions of said organic components so asto produce short chain fatty acids; d) forming a solids blanket ofbiomass in said second anaerobic region; e) flowing said wastewater insaid second anaerobic region upwardly through said solids blanket; f)returning liquid from said second anaerobic region with said short chainfatty acids therein to said first anaerobic region wherein phosphorus isreleased from microorganisms in said biomass in said mixed liquor andshort chain fatty acids are taken up by the microorganisms in saidbiomass; g) thereafter flowing the mixed liquor from said firstanaerobic region to an aerobic region wherein said short chain fattyacids are metabolized by said microorganisms in said biomass andphosphorus is absorbed by said microorganisms; h) thereaftertransferring said mixed liquor to a clarifier region wherein clarifiedliquid is separated from said biomass; and i) returning at least aportion of the separated biomass with phosphorus therein to said firstanaerobic region.